Known processes for producing 4a-aryl-trans-decahydroisoquinolines, especially, 6-oxo compounds, include the method of Rapoport et al. (U.S. Pat. No. 4,189,583, J. Org. Chem. 42, 1485, 1977), the method of Zimmerman et al. (J. Org. Chem. 54, 1442, 1989) and the method of Judd et al. (J. Med. Chem. 35, 48, 1992).
A key step utilized in the present invention, that is, the step of introducing an aromatic ring employs the 1,4-conjugate addition reaction to an enone compound (II) using an aromatic metal compound represented by aromatic copper compounds. A process for producing 4a-aryl-6-oxodecahydroisoquinolines utilizing a reaction similar to this reaction is known (J. Org. Chem. 39, 1118, 1974., U.S. Pat. No. 4,301,290). That is, in this process, a compound of the formula (XI) ##STR1## is reacted with a aromatic copper complex to produce a 4a-aryl-6-oxodecahydroisoquinoline of the formula (XII). ##STR2## However, the condensed ring moiety of the compound produced by this process has the cis configuration, and the trans isomers which the invention aims at producing cannot be obtained by this process.
Further, it is known that among the 4a-aryldecahydroisoquinoline compounds, the compounds having a condensed ring with cis configuration are thermodynamically stable than the compounds having a condensed ring with trans configuration.